Nano-sized CuInS2 was evenly anchored on the thin film of reduced graphene oxide (rGO/CuInS2) by a simple one-step solvothermal method. The photocatalytic activity of rGO/CuInS2 was much higher than that of pure CuInS2, and was highly dependant on rGO amount with results revealing an optimal rGO content of 1 wt%. The 1% rGO/CuInS2 composite demonstrated the highest visible-light photocatalytic activity with almost 90% 2-nitrophenol removal, which was almost two times of pure CuInS2. The enhanced photocatalytic activity of rGO/CuInS2 is ascribed to that the ultrathin film structure of rGO endows rGO/CuInS2 composites with a large density of exposed active sites to reactants, short transport distances of photogenerated charges and the efficient separation of charge carriers. Of special significance is that 1% rGO/CuInS2 composite can effectively treat real pharmaceutical wastewater with 86.5% chemical oxygen demand (COD) removal efficiency in 11 h. Moreover, there was no obvious decrease in the photocatalytic activity of rGO/CuInS2 composites after four photocatalytic cycles. The high COD removal efficiency of pharmaceutical wastewater and reusability indicate the great potential of rGO/CuInS2 in environmental purification of organic pollutants.